Urethane Casting Design Guidelines

Design Guidelines for Urethane Casted Parts

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Urethane castings are excellent choices for production-grade plastic parts without the cons of expensive hard tooling, design complications, and delayed turnaround periods. When designing cast urethane, it is imperative to stick to some basic guidelines. These rules are important to ensure that your part functionality and production lead times remain intact. To help you create master patterns that match your desired specifications and function as intended, Premium Part Manufacturing Solutions have put together these simple but actionable tips to help design higher-quality urethane casted parts.

1. Keep the walls uniform

As is the case in the most manufacturing process, maintaining uniformity in wall thickness is equally important for a dimensionally stable urethane casted part. The wall thickness of your cast urethane part should be consistent all-round the part to enable the molten urethane to flow into the mold and cure at a uniform rate.

Designing parts with varying wall thickness can cause parts to fail, inhibit functionality and even result in a total product defect on production. The design guideline recommended for wall thickness is to have them at least 0.020&#;&#; &#; 0.050&#;&#;. This range can be defined as at least 0.20&#;&#; for smaller parts and at least 0.40&#;&#; for larger parts. Remember that the wall thickness should be consistent with the size of the product to provide the required support. Most parts have their average wall thickness ranging from 0.80&#;&#; to 0.150&#;&#;.

2. Draft angles and Undercuts

Unlike injection molding, urethane castings designs need not place much emphasis on drafts. This is because liquid urethane is free-flowing and will take the shape of any mold to be used in production. To mitigate the risks of breaking and warpage however, consider using at least one degree of a draft for your cast urethane part. This will also aid the extraction process when removing the final part from the mold.

3. Factor in shrinkages

Shrinkages are very natural in urethane casting and metal die-casting operations. They naturally occur as a result of a change in the density between the liquid urethane and the solidified part. Because of this, the final dimensions of any cast urethane part will largely depend on the precision and allowance put into the design of the master model. For best results, you must factor in some percentage as shrinkage rate. This number often ranges between 0.10 to 0.20%.

4. Consider accessibility and manufacturing

Having a firm understanding of your design, the important, functional and purely aesthetic features can go a long way in helping you attain the best master model. Before incorporating certain features into your design, evaluate the importance of the feature and how such feature can have an impact on the functionality and moldability of your final part. As for corners, try to use radii of at least 0.125&#;&#; to ensure that your part remains strong and mold flow remains seamless. For the boss corners, radii considerations should be around 0.060&#;&#; to retain part strength even at slightly lower wall thickness. For part tolerances, keep your urethane casting design within +/- 0.010&#; for the first inch and half of that for every subsequent inch.

As much as possible, try to do away with design features that may simply complicate the mold flow or increase lead times and overall production cost.

5. Finishing considerations

Finally, considerations around finishing are very important with cast urethane parts. This is because urethane castings can be made in a variety of finishes. The standard finishes include matte and sanded, however, polished surfaces, lettering, embossing, or engraving may come at some extra cost.

If your urethane-casted parts are to be lettered, ensure that the logo or lettering is at least 0.040 inches thick. It should also be elevated to this same dimension for the raised visual effect or lowered likewise for a sunk-in, recessed effect.

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Understand what is urethane casting, process of casting urethane as well as its benifits and applications.

Introduction

The purpose of this article is to offer a comprehensive understanding of urethane casting, its materials, and the detailed process involved.

We will also compare urethane casting with injection molding and discuss the applications and advantages of urethane casting.

What is Urethane Casting

Definition of Urethane Casting

Urethane casting, also known as vacuum casting, is a versatile manufacturing process that involves creating parts by pouring liquid urethane into a mold, which then hardens into the desired shape.

This method is particularly effective for producing prototypes, small production runs, and parts that require detailed features.

Urethane casting is known for its ability to produce high-quality, detailed parts quickly and cost-effectively without the need for expensive tooling.

Urethane Casting vs. Injection Molding

Aspect

Urethane Casting

Injection Molding

Production Volume

Low to medium

High

Cost

Lower upfront costs

Higher upfront costs

Lead Time

Shorter

Longer

Ideal For

Prototypes, small runs

Large-scale production

Urethane Casting vs. Injection Molding

Production Volume

Urethane casting is ideal for low to medium production volumes, commonly ranging from a few units to several hundred parts. This makes it excellent for prototyping, custom parts, and limited runs.

Injection molding, however, suits high-volume production, typically involving thousands to millions of parts.

Cost

Urethane casting has lower upfront costs due to cheaper silicone molds compared to the expensive steel molds of injection molding. This cost-effectiveness is beneficial for smaller runs where high injection molding costs aren't justified.

Despite higher per-part costs, overall expenses for low to medium volumes are lower in urethane casting.

Lead Time

Urethane casting offers shorter lead times, beneficial for rapid prototyping and quick turnarounds.

Silicone mold creation is faster and simpler than the metal molds needed for injection molding, resulting in a quicker design-to-production timeline. Injection molding's longer setup time is due to the complexity and precision required in mold creation.

Overall, urethane casting provides a flexible, cost-effective, and fast solution for low to medium volume production, ideal for creating detailed and high-quality parts.

Urethane Casting Materials

Urethane casting involves the use of two main categories of materials: those required for the mold and those required for the production process.

Materials Required for the Mold

• Silicone Rubber: Silicone rubber is commonly used to create molds for urethane casting due to its flexibility, durability, and ease of use. Silicone molds can capture intricate details and are reusable for multiple casting cycles.

• Release Agents: Release agents are applied to the mold surface to prevent the urethane casting resin from sticking to the mold. They ensure easy demolding and help prolong the lifespan of the silicone mold.

Materials Required for the Production Process

Urethane Casting Resin

• Urethane casting resin is the primary material used to create the actual parts. It is a versatile polymer known for its durability, flexibility, and ability to mimic the properties of production-grade plastics.

• This resin offers versatile properties, adaptable for diverse applications, crafting both rigid and flexible parts as needed. Common variants like ABS-like, PC-like, and rubber-like resin mimic ABS plastic, polycarbonate, and rubber, respectively, ensuring durability, clarity, and flexibility.

Additives and Fillers

Urethane casting compounds often include various additives and fillers to enhance specific material properties.

These additives can include:

• Rigidity Enhancers: Additives made of materials like glass or mineral fillers that increase the stiffness of the urethane casting resin, making it suitable for structural applications.

• Clarity Enhancers: Additives such as transparent resins or nanoparticles that improve the optical clarity of the resin, ideal for applications requiring transparency or specific optical properties.

• Thermal Stabilizers: Additives like heat-resistant polymers or ceramics that improve the thermal resistance of the resin, enabling it to withstand high temperatures without degrading.

By adjusting the formulation with these additives, manufacturers can customize the urethane material to meet the precise requirements of different projects, ensuring optimal performance and quality in the final parts.

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Process of Casting Urethane

The urethane casting process involves several key steps to produce high-quality parts with detailed features.

Below is a detailed breakdown of each step, along with illustrative images to enhance understanding.

Process of Casting Urethane
Source: firstpart.com

Step 1. Mold Creation

A master pattern is created, usually via 3D printing or CNC machining, which serves as the template for the silicone mold.

The master pattern is carefully designed to ensure that the final part will have the desired shape and details.

Step 2. Mixing Urethane

The urethane resin is mixed with a curing agent, following precise ratios to ensure the proper material properties.

This mixture must be homogeneous to avoid inconsistencies in the final part.

Step 3. Pouring

The mixed urethane is poured into the silicone mold.

This step is often done under vacuum to eliminate air bubbles, which can cause defects in the final part.

Ensuring a bubble-free pour is crucial for achieving a smooth and accurate surface finish.

Step 4. Curing

The filled mold is placed in an oven or left at room temperature to cure, solidifying the urethane.

The curing time and conditions depend on the specific urethane formulation and the desired properties of the final part.

Step 5. Demolding

Once cured, the mold is carefully opened to remove the finished part.

The silicone mold is flexible, which helps in releasing the part without damaging it.

Proper demolding techniques are essential to maintain the integrity of both the mold and the cast part.

By following these steps and using the appropriate tools, urethane casting can produce high-quality, detailed parts suitable for a wide range of applications.

Types of Urethane Castings

Urethane casting can produce a variety of part types, each tailored to meet specific requirements and applications.

Here are the primary types of urethane castings, along with their distinct properties and uses.

Rigid Urethane Castings

Rigid urethane castings are used for parts requiring structural integrity and stiffness.

These parts can withstand high stress and are often utilized in applications where durability and load-bearing capabilities are essential.

• Applications: Mechanical components, housings, brackets, and structural supports.

• Properties: High strength, durability, and dimensional stability.

Flexible Urethane Castings

Flexible urethane castings are ideal for parts that need flexibility and impact resistance.

These parts are designed to absorb shock and maintain their shape under stress, making them suitable for dynamic applications.

• Applications: Gaskets, seals, bumpers, and protective covers.

• Properties: High flexibility, impact resistance, and elasticity.

Clear Urethane Castings

Clear urethane castings are utilized in applications requiring transparency or specific optical properties.

These parts are often used where visibility and aesthetic appearance are important.

• Applications: Lenses, display components, prototypes, and custom lighting fixtures.

• Properties: Optical clarity, UV stability, and smooth surface finish.

Each type of urethane casting offers unique benefits, making urethane a versatile material for a wide range of industries and applications.

By selecting the appropriate type of urethane casting, manufacturers can ensure that their parts meet the specific needs of their projects.

Applications of Urethane Casting

Urethane casting offers versatility across various industries, making it suitable for a broad range of applications:

Prototyping

Urethane casting enables the creation of functional prototypes with production-like quality.

This allows manufacturers to test and iterate designs before committing to full-scale production, accelerating the product development process.

Functional Prototypes
Source: prototypes.prioritydesigns.com

Short-Run Production

Cost-effective for producing limited quantities of parts without investing in expensive tooling.

This makes urethane casting an ideal solution for small production runs, where traditional manufacturing methods like injection molding may not be economically viable.

Short-Run Productions
Source: prototypes.prioritydesigns.com

Industrial Applications

Urethane casting is widely used in industrial settings for manufacturing machinery parts, protective covers, and custom components.

Its versatility and durability make it suitable for various applications where strength and reliability are paramount.

Polyurethane Protective Covers
Source: precisionurethane.com

Consumer Products

Commonly found in custom enclosures, toys, and decorative items.

Urethane casting allows for the production of aesthetically pleasing and functional consumer products with intricate details and high-quality finishes.

Urethane Cast Magical Girl Design Toy with ABS-like Resin
Source: facfox.com

From prototyping to short-run production and industrial to consumer applications, urethane casting offers a cost-effective and versatile solution for creating high-quality parts across diverse industries.

Advantages of Urethane Casting Parts

Parts produced via urethane casting offer several significant benefits:

Cost-Effectiveness

Urethane casting requires a lower initial investment compared to other manufacturing processes like injection molding.

The cost of creating molds for urethane casting is significantly lower, making it a cost-effective solution for producing small to medium volumes of parts.

Versatility

Urethane casting is highly versatile and can accommodate a wide range of materials and part designs.

Whether producing rigid or flexible parts, urethane casting can meet diverse project requirements, making it suitable for various industries and applications.

Precision and Detail

Urethane casting is capable of producing intricate and highly detailed parts with excellent dimensional accuracy.

This precision allows for the creation of complex geometries and fine features, making it ideal for applications where tight tolerances are required.

Durability

Urethane parts are robust and can withstand various environmental conditions, including temperature fluctuations, moisture, and chemicals.

This durability ensures that urethane castings maintain their structural integrity and performance over time, making them suitable for demanding applications in industries such as automotive, aerospace, and electronics.

Overall, the cost-effectiveness, versatility, precision, and durability of urethane casting make it a preferred manufacturing method for producing high-quality parts across a wide range of industries and applications.

Conclusion

Urethane casting is a highly adaptable and efficient manufacturing process, particularly beneficial for prototyping and low to medium volume production.

It offers significant advantages in terms of cost, versatility, and speed compared to traditional injection molding.

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Whether used for prototyping or short-term production, Unionfab can provide reliable solutions for your manufacturing needs.

Also, we can provide various types of services you may need, such as vacuum/urethane casting and injection molding mentioned in this article.

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If you want to learn more, please visit our website Urethane Casting Services.